The present invention relates to a device for coating of workpieces, with an application unit having a distributing plate provided with at least one nozzle and at least one valve unit.
Such coating devices are used for example for coating of electric chips utilized in smart cards. The chips are arranged in a row or several rows on a support film. In these applications, very small, exactly defined quantities of coating material must be applied on the individual chip. At the same time, verify accuracy requirements for the coating device are applicable. In known coating devices with diaphragm valves, during opening and closing of the valve which provides dosing of the coating quantity, the material is displaced, and it is possible that the coating quantity is not dosed with the required accuracy. Significant deviations in the supply passages which guide the coating material produce an undesirable air cushion which is difficult to eliminate. When different materials must be treated, then under certain conditions the coating devices or parts of the devices must be exchanged with other which are adapted to these materials. The utilization of glass fiber-filled coating materials can lead to clogging of such valves.
Accordingly, it is an object of present invention to provide a device for coating of workpieces, which are improved so that they eliminate the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a device for coating of workpieces with an application unit, which has at least one distributing plate provided with at least one nozzle and at least one valve unit, wherein the at least one valve unit is formed as a plate valve (or a single-face valve) with at least one inlet slider and at least one outlet slider.
With the inventive device, before the application of the coating material the material is dosed in the application unit. For dosing, the at least one inlet slider is opened and the at least one outlet slider is closed. Subsequently for application of the coating material, the inlet slider is closed and the outlet slider is opened. In this manner the back displacement of the material or the droplet formation are avoided. Furthermore, the at least one inlet slider and the at least one outlet slider when necessary can be exchanged. This provides for substantially lower mounting expenses for than existing mounting and dismounting valves.
At least one intermediate plate with at least one material-guiding passage is provided for dosing of the material quantity between the at least one inlet slider and the at least one outlet slider. The at least one material-guiding passage is filled during dosing of the coating material, and is emptied during the subsequent coating.
The valve unit can be provided with at least one pressing plate which is loaded with a tensioning module and has at least one material-guiding passage. Thereby the at least one inlet slider and the at least one outlet slider which are susceptible to wear can be post-treated on their surface, and subsequently despite their reduced thickness, provide a tight closure.
The tightening module can be formed as a cylinder-piston device. In this case it operates simultaneously and has a long-term stability. The tightening module can produce a stroke-independent tensioning force.
At least one opening which receives a piston can be provided in at least one intermediate plate and laterally open into the at least one material-guiding passage. By withdrawing of the at least one piston, the volume of the at least one material-guiding passage in the at least one intermediate plate can be increased. During dosing of the coating material in the at least one material-guiding passage of the intermediate plate, the at least one opening which receives the piston can be released by a lateral displacement of the piston. Thereby the dosed coating material can be supplied in the opening which receives at least the one piston. During application of the coating material, the piston is moved in the opposite direction and thereby the coating material is displaced from the opening which receives at least one piston. The piston, depending on the application and the utilized material, can be pulled more or less, and thereby the flexibility of the device is increased.
The end side of the piston which faces the at least one material-guiding passage can be adjusted to the curved course of the wall of the material-guiding passage. Therefore an insertion of the piston in the material-guiding passage of the intermediate plate is avoided, which can lead to air pocket under the piston in the material-guiding passage. Advantageously, the at least one piston can be driven by a motor, and can be provided with a control, so that a compensation of the material decompression is performed. As a result, during opening of the inlet slider the material is supplied under pressure into the piston openings and the material guiding passage, or in other words compressed, and after opening of the outlet slider is relaxed. This can lead to droplet formations or to a greater material discharge.
The piston receptacle of the at least one piston can be coupled with the piston drive plate in direction toward the piston axis with the intermediate plate. Therefore with the post-treated plates of the at least one inlet slider and at least one outlet slider, the at least one piston can follow the new position of the intermediate plate. The above mentioned coupling can be formed for example through at least one eccentric shaft. The eccentric shaft presses the piston receptacle in direction of the piston longitudinal axis against the drive plate.
In order to avoid air inclusions in the material-guiding passage, the material-guiding passage can be guided so that the material performs deviation by at most 90xc2x0.
For reducing the wear of the sealing surfaces of the at least one inlet slider and the at least one outlet slider, the outer surface of the at least one inlet slider and the at least one outlet slider can be provided with projecting sliding regions.
In the event of wear of the sliding regions, in order to avoid exchanging of the complete inlet slider, outlet slider, the at least one intermediate plate, and the at least one pressing plate, these sliding regions can be formed as exchangeable inserts.
For avoiding air inclusions, the material-guiding passages can also reduce from the material inlet to the material outlet.